Throughout the specification (including in the claims) the terms "video data" and "video signal" are used to denote any of the broad class of image signals indicative of pixels of an image, including analog image signals and digital image signals.
Throughout the specification (including in the claims) the expression "disk storage device" is used to denote any of the broad class of devices which store data on one or more magnetic, optical, magneto-optic, or other disks. The term "disk" is used to denote any of such disks.
Throughout the specification (including in the claims) the expressions "external storage device" and "storage device" are used interchangeably to denote a storage device which is a member of the broad class of storage devices capable of storing compressed (or otherwise processed) data, and which is separate from a compression circuit or other processing circuit (including any buffer memory associated therewith) employed to generate the compressed (or otherwise processed) data to be stored therein. For example, disk storage device 14 (shown connected along bus 18 in FIG. 2) is an external storage device, capable of storing compressed video data generated in codec circuit 8 within circuit 6. Device 14 includes one or more magnetic, optical, magneto-optic, or other disks (the term "disk" is used to denote any of such disks).
Many methods and apparatus for compressing digital video data have been developed. An important class of conventional methods for digital video compression are compression methods which employ adaptive rate control to limit the output data rate (the rate at which compressed data are output) to a fixed value. Examples of conventional digital video compression methods with adaptive rate control are described in U.S. Pat. No. 5,231,484, issued Jul. 27, 1993 to Gonzalez, et al., U.S. Pat. No. 5,253,078, issued Oct. 12, 1993 to Balkanski, et al., and U.S. Pat. No. 4,394,774 issued Jul. 19, 1983 to Widergren, et al.
FIG. 1 is a block diagram of a typical conventional system for implementing digital video compression with adaptive rate control. In FIG. 1, compression/decompression ("codec") circuit 2 receives video data from video source 3, and can process the video data to generate compressed video data and then output the compressed video data to buffer memory 4. Buffer memory 4 has a fixed capacity. The compressed video data are then output from buffer 4 over a system bus. A video disk storage device (not shown) is typically connected along the bus for storing the compressed video data. Codec circuit 2 monitors the amount of buffer 4's capacity filled with compressed video data (the value X%, indicated in FIG. 1), and adjusts the flow rate of compressed video pixels into buffer 4 such that buffer 4 is never completely full or completely empty (to ensure that compressed data are output from buffer 4 to the system bus at a preselected constant rate).
Codec 2 and buffer 4 of FIG. 1 are typically implemented as a single piece of hardware (often a single integrated circuit). Compressed data are written to a storage device (connected along the system bus) from buffer 4 at a preselected fixed rate, to provide a controlled output bandwidth to the system bus from the hardware in which buffer 4 is implemented.
However, conventional video compression methods which implement adaptive rate control (including those of the type described with reference to FIG. 1), have serious limitations. One such limitation is that their output bandwidth cannot be automatically and adaptively controlled to maintain transfers of compressed video data therefrom to any of a variety of compressed video data storage devices (or other devices) with an optimal (e.g., maximum attainable) bandwidth which depends, in general, on the particular data storage device receiving the compressed video data signals.